1. Field of the Invention
The present invention relates to an imaging system and an optical engine, and more particularly, relates to an imaging system and an optical engine of a Non-Telecentric configuration.
2. Descriptions of the Related Art
Projection apparatuses have been widely used in governmental offices, companies, academic institutes and even at homes due to the decreasing costs over the years as a result of the advancement and market competition of the hi-tech industry. Among these projection apparatuses, the digital light processing (DLP) projection apparatuses is gradually replacing other projection apparatuses as the mainstream product. Because the DLP projection apparatus employs a digital micromirror device (DMD) as the primary element for processing and imaging a light ray from a light source into an image, luminance is improved and less exhaust heat is generated by the projection apparatus.
The conventional DLP projection apparatus (not shown) typically adopts an optical engine (not shown) of a Non-Telecentric configuration in an attempt to cut down the cost. As shown in FIG. 1, the optical engine comprises an imaging system 11, which further comprises a lens assembly 111, a DMD 113 and a reflective mirror 114. To simplify the structure of the light path, the imaging system 11 further comprises an aspheric lens 112 for focusing a light ray 10 onto the DMD 113. As shown, a light ray 10 received by the imaging system 11 is reflected by the reflective mirror 114 into the aspheric lens 112, which focuses the light ray 10 onto the DMD 113. Then, the light ray 10 is reflected by the DMD 113 into the lens assembly 111 to project the image. However, since the angle between the illumination section (from the DMD 113 towards the aspheric lens 112) and the imaging section (from the DMD 113 towards the lens assembly 111) in the light path is very small, the space is closely packed, causing mechanical interference of the aspheric lens 112 with the lens assembly 111. Consequently, in practice, the aspheric lens 112 must cut off a portion thereof to form a depression 112a for receiving a portion of the lens assembly 111. Because the aspheric lens 112 has a substantial thickness, the sectional surface forming the depression 112a also has a substantial area. Consequently, due to the arrangement angle, a portion of the light 10 impinged on the aspheric lens 112 will subject to total reflection (not shown) from the inner side of the sectional surface of the depression 112a and scattered into stray light which is hard to handle. The scattered stray light then enters into the lens assembly 111, which causes poor imaging quality.
Conventional designs have attempted to prevent the light ray 10 from impinging on the depression 112 and the inner side of the sectional surface thereof. Unfortunately, this may decrease the area where the light ray 10 impinges on the aspheric lens 112, i.e., to decrease the efficiency for utilizing the aspheric lens 112, thus adversely affecting the luminance performance of the optical engine. In view of this, efforts still have to be made in the field to mitigate the scattered stray light generated due to the use of the aspheric lens 112.